Radio signaling system



17, 1931. R s, QHL 1,792,600

RADIO SIGNALING SYSTEM Filed Sept. 23, 1925 722 Signaling CircuitINVENTOR R61 OM WL ATTORNEY Patented Feb. 17, 1931 UNITED. STATES:

PATENT OFFICE.

EcssELL s. OHL, OF NEW Yon-K, 'N. Y., AssIaNon 'ro AMERIGAN TELEiEHONEAND V TELEGRAPH COMPANY, A CORPORATION on NEW YORK' RADIO SIGNALI GsYs'rEM Application filed September 23,1925. :SeriaI No. 58,165.

This invention relates to radio signaling systems, and more particularlyto systems wherein two or more high frequencies are transmitteduponwhich thesame signals are simultaneously superimposed.

It has been thepractice heretofore to transmit signals between twostations a considerable distance apart by means of a single highfrequency wave, the signals being superim posed thereupon. But in suchsystems the signals very ofted faded away on account'of the effect ofthe condition of the atmosphere thereon. It hasbeen due to this fadingeffect that signals were sometimes completelylost 1 during shortperiods, causing mistakes in the record'during thos'e'periods.

It is therefore an object of this invention to provide a system in whichtwo or more high frequencies are employed, the signals beingsimultaneously superimposed on all of said highfrequencies, so that whenone of the high frequencies upon which signals are superimposed fadesaway another high frequency upon which the signals are superimposed willbe transmitted to the distant station unaflected by atmosphericconditions. The method and means by which this object is accomplishedconstitute one of the novel features of this'invention. Other objectsand features of this invention will be better understood from thedetailed description hereinafter following when read in connection withthe accompanying drawing showing one embodiment of the inven tionsuitable as a radio telegraph system.

Referring to the drawing, two stations A and B are shown. At station Athere are two high frequency oscillation generators O and 0 which arecontrolled as to frequency by 40 piezo-electric devices PE and PE Thesepiezo-electric devices PE and PE render the oscillations of the highfrequency oscillation generators O and O constant within narrow limits.The frequency of these oscillation generators O and 0 may be, forexample 1,000,000 and 1,000,100 cycles. The output circuits of theseoscillation generators are respectively connected to the input circuitsof three-electrode vacuum tubes T and T 59 A source of potential asupplies the necessary vacuum tubes T and T 'to anfy 'preferablyharmonics of the r space current to the anodes of'vacuum tubes T and Tthrough an alternating current choke coil 5. The output circuits of thevacuum tubes T and T foralternating currents include the inductance 0and the condenser at (said inductance and condenser being in common tosaid circuits) and the anode and cathode of the respective vacuum tubesT, and T The variable-condenser e is employed for tuning the outputcircuits of these frequencies, equencies in theinput circuits of thesetubes, for example, 2,000,000 and 2,000,200 cycles, respectively.

The input circuit of'an amplifier A is cou- 'pled by means ofinductances f and c to the output circuits of the'vacuum tubes T and TBecause of this coupling, the same frequencles are impressed ontheiinput circuit of the amplifier A as are present in the out-' putcircuits of vacuum'tub'es T and T The source of potential 9 supplies thenecessary space current to the anode of the amplifier A in the circuitincluding the inductance h, the anode and cathode of the amplifier A andthe source of potential 9; The variable condenser j and the inductanceiare connected across the anode and grid control electrode of theamplifier A in order to neutralize the electrostatic capacityexistingbetween said electrodes. The variable condenser k is employedfor tuning the output circuit ofthe amplifier A to any frequencies, forexample, 2,000,000 and 2,000,200 cycles, the tuning of this outputcircuit being broad enough to include both frequencies.

A heavy resistance 1" is connected to the input and output circuits ofthe amplifier A in common to said circuits. A relay having a winding Zand an armature m is employed for superimposing signals on the highfrequencies present in the input circuit of the amplifier A The windingZ of this relay may be connected to a source of potential and atelegraph key, or any other means for making and breaking the currentflowing in the winding Z. When current flows through the winding Z, thearmature m will be attracted and will. close its contact to shunt theresistance 1', Thus the two high frequencies in the input circuit of theamplifier A will be amplilied by the amplifier A and will appear in theoutput circuit thereof. hen no current flows through the winding Z, thearmature on will be released opening its contact and permitting theresistance 1' to be connected in common in the input circuit and in theoutput circuit of the amplifier A Thus the grid control electrode of theamplifier A will be made highly negative with respectt-o the cathode andwill prevent the high frequencies present in the input circuit of theamplifier A from being amplified thereby. Signals that cause the windingZ to become energized and deenergized permit the high frequencies to bealternately transmitted-and then suppressed by the amplifierA Theinductance n is loosely coupled to the inductances h and i in order topermit the high frequencies in the output circuit of the amplifier Aupon which signals are superimposed to be transmitted to the antenna 0.I

At station B an antenna p and an inductance g are tuned so as to receivethe high frequencies modulated in accordance with signals transmitted bythe antenna 0 at station A. These high frequencies are then impressed onthe input circuit of the detector D Another oscillation generator 0 iscoupled to the input circuit of the detector D in order to provide afrequency which isto beat with the received high frequencies in theinput circuit of the detector D This oscillation generator 0 may be anoscillation generator of any well known type, preferably a vacuum tubeoscillation generator suitable for transmitting oscillations at veryhigh frequency. For the sake of simplicity this oscillation generator 0will have oscillations of a frequency, of, for example, 2,000,100cycles, half way between the high frequencies transmitted by station Aupon which signals are superimposed.

All of these frequencies beat in the input circuit of the detector D toproduce in the output circuit of the detector 1),, among otherfrequencies, the difference frequency of 100 cycles. The transformer stransmits frequencies in the output circuit of the detector D to theinput circuit of an-amplifier A This amplifier has a variable condensert associated with the input circuit thereof in order to permit onlythediiference frequency of 100 cycles to be transmitted thereby to theexclusion of the higher frequencies. This low frequency is amplified bythe amplifier A and appears in amplified form in the output circuitthereof; Another transformer 16 is employed for impressing thisamplified low frequency on the input circuit of a vacuum tube rectifierR. The rectified current energizes the winding of a relay o, thearmature of which is w, so as to transmit the signals represented by therectified current to the channel operated by the armature w. A condenser3 is connected in the output circuit of the vacuum tube rectifier R toform a path of low impedance for any alternating current that may appearin the output circuit of said rectifier.

The arrangements of this invention operate in the following manner forthe transmission of signals from station A to station B.

Two high frequencies, for example, 1,000,000 and 1,000,100 cycles, areset up by the oscillatorsO and 0 respectively, these high frequenciesbeing controlled as to frequency by the pieZo-electric devices PE and PEThese high frequencies are impressed on the input circuits of the vacuumtubes T and T the output circuits of these vacuum tubes being tuned toharmonics of the frequencies in the input circuits of these tubes, forexample, 2,000,000 and 2,000,200 cycles, respectively. These two highfrequencies are then impressed on the input circuit of the amplifier ASignals are also transmitted to the input circuit of the amplifier A bymeans of the winding 1 and the armature m of a relay connected to asignaling circuit. These signals are simultaneously superimposed on bothhigh frequencies, and these high frequencies upon'which the signals arethus superimposed appear in the output circuit of the amplifier AThereafter they are transmitted to the antenna 0 for transmission tostation B.

The antenna-p at station B is tuned to-receive the high frequencies uponwhich signals are superimposed which are transmitted by the apparatus atstation A. These frequencies are then'impressed on the input'circuit ofthe detector D There are also impressed on the input circuit of thedetector D the oscillations of an oscillation generator which has afrequency of, forexample, 2,000,100 cycles, half way between thefrequencies upon which the same signals are simultaneously superimposedat station A. These three high frequencies beat in the input circuit'ofthe detector D to produce a difference frequency of 100 cycles in theoutput circuit thereof. This low frequency is amplified by the amplifierA and theother higher frequencies are eliminated. After amplification bythe amplifier A the low frequency is transmitted to the rectifier Rwhich has the winding o of a relay connected in the output circuitthereof. This winding 1) becomes energized in accordance with rectifiedsignals, so that the signals may be im-- pressed on a channel operatedby the armature w of this relay.

The frequencies used herein are merely for purpose of illustration, andin practice other frequencies may be employed as conditions necessitate.

lVhile the arrangements of this invention have been disclosed withparticular reference to a radio telegraph system, it is to beundel'stood that it is capable of embodiment in a radio, telephone system,among other systems, for the transmission of voice frequencies, thefrequencies employed for transmission upon which voice frequencies areto be superimposed differing from each other by a .frequency above thelimits of audition;

It will be understood that while only'two frequencies have been employedfor transmission upon which signals are simultaneously superimposed, theinvention is not so limited,

but any number of high frequencies may be employed, the signals beingsimultaneously superimposed on all of said frequencies.

VVhilethis invention is disclosed in one particular embodiment which isdeemed desirable, it is to be understood that it is capable ofembodiment in other and widely varied organizations without departingfrom the spirit of the invention andthe scope of the appended claims.

What is claimed is:

1. The method of signaling which consists in interrupting two sinusoidalcurrents of high frequencies simultaneously in accordance with signals,amplifying said interrupted high frequencies, heating with saidinterrupted high frequencies sinusoidal current of another highfrequency midway between said two high frequencies so as to obtain a lowfrequency current interrupted in accordance with said signals,amplifying said low frequency current thus interrupted, and rectifyingsaid interrupted low frequency current so as to obtain the signalstherefrom.

2. In a radio signaling system, in combination, means for generating twosinusoidal currents of different high frequencies, means forsimultaneously interrupting and thereby modulating said high frequenciesin accordance with telegraphic signals, means for generating sinusoidalcurrent of a third high frequency midway between said two highfrequencies which are interrupted and which is to be beaten with saidhigh frequencies, means for beating all of said high frequenciestogether so as to obtain a low frequency current interrupted andmodulated in accordance with said signals, and means for deriving thesignals from said low frequency current.

3. The method of signaling which consists in beating a pair ofsinusoidal currents of high frequencies both modulated in accordancewith the same signals with sinusoidal current of another high frequencymidway between said pair of high frequencies so as to obtain current ofa low frequency, said low frequency being modulated in accordance withsaid signals, and deriving the signals from said low frequency.

4. A radio signaling system comprising a transmitting station and areceiving station, the transmitting station comprising means forgenerating two sinusoidal waves of high imposed so as to obtain a.subaudible frequency upon which said signals are superimposed, and meansto derive the signals from saidsubaudible frequency.

5. A radio signaling system comprising a transmitting station and areceiving station,

the transmitting station comprising means for generating two sinusoidalcurrents of high frequencles, means for simultaneously superimposlng thesame signals on said high frequencies, and means for transmitting saidhigh frequencies upon which said signals are superimposed, the receivingstation comprising means for receiving said high frequencies upon whichsaid signals are superimposed,

means for generating a sinusoidal current havlng a frequency locatedbetween said two received high frequencies, means for beating said highfrequency with the receivedhigh frequencies upon which said signals aresuperimposed so as to obtain a low frequency upon which said signals aresuperimposed, means for transmitting said low frequency upon which saidsignals are superimposed to the exclusion of all higher frequenciesresulting from modulation, and means for detecting the signals from saidlow frequency.

6. A radio signaling system comprising a transmitting station and areceiving station, the transmitting'station comprising means forgenerating a pair of sinusoidal currents of high frequencies, means forsimultaneously interrupting the currents of said high frequencies inaccordance with telegraphic sig,

nals so that said signals may become superimposed thereon, and means fortransmitting said high frequencies upon which said signals aresuperimposed, the receiving station comprising means for receiving saidhigh frequencies upon which said signals are superimposed, means forgenerating a sinusoidal current of high frequency midway between thefrequencies of the pair of currents generated at the transmittingstation, means for beating said high frequency with the received highfrequencies upon which said signals are superimposed so as to obtain alow frequency current modulated by said signals, means for filtering theproducts of beating so as to eliminate all frequencies higher than saidlow frequency, and means to detect the signals from said low frequency.

7. A radio rece1v1ng' system comprising means for receiving a pair ofdifferent high frequencies modulated in accordance With signals, both ofsaid high frequencies being modulated by the same signals, means forgenerating a high frequency midway between said received highfrequencies, means for beating said generated high frequency with saidreceived high frequencies modulated in accordance With said signals soas to obtain-a difference frequency, said difference frequency beingmodulated in accordance with the same signals, and means for derivingthe signals from said difference frequency.

8. A radio receiving system comprising means for receiving two highfrequencies each interrupted and thereby modulated in accordance withthe same signals, means for generating a high frequency midway betweensaid two high frequencies, means for beating said generated high'frequencywith said received high frequencies modulated in accordancewith signals so as to produce a subaudible frequency modulated by thesame signals, means for suppressing all frequencies except thesubaudible frequency modulated by said signals, and means for detectingthe signals from said subaudible frequency.

In testimony whereof, I have signed my name to this specification this21st'day of September, 1925.

RUSSELL S. OHL.

